The present invention relates to magnetoresistive read sensors for reading signals recorded in a magnetic medium, and more particularly, this invention relates to improving gap layers of a magnetoresistive read sensor to optimize operating characteristics.
Computer systems generally utilize auxiliary memory storage devices having media on which data can be written and from which data can be read for later use. A direct access storage device (disk drive) incorporating rotating magnetic disks is commonly used for storing data in magnetic form on the disk surfaces. Data is recorded on concentric, radially spaced tracks on the disk surfaces. Magnetic heads including read sensors are then used to read data from the tracks on the disk surfaces.
In high capacity disk drives, magnetoresistive read sensors, commonly referred to as MR heads, are the prevailing read sensors because of their capability to read data from a surface of a disk at greater linear densities than thin film inductive heads. An MR sensor detects a magnetic field through the change in the resistance of its MR sensing layer (also referred to as an xe2x80x9cMR sensorxe2x80x9d) as a function of the strength and direction of the magnetic flux being sensed by the MR layer.
FIG. 1 illustrates a cross-sectional view of an MR head, in accordance with the prior art. As shown, an MR read head includes an MR sensor which is sandwiched between first and second gap layers G1 and G2 which are in turn sandwiched between first and second shield layers S1 and S2. Lead layers are sandwiched between the first and second gap layers for providing a sense current to the MR sensor. Magnetic fields from a magnetic disk change the resistance of the sensor proportional to the strength of the fields. The change in resistance changes the potential across the MR sensor which is processed by channel circuitry as a readback signal.
An MR read head is typically mounted to a slider which, in turn, is attached to a suspension and actuator of a magnetic disk drive. The slider and edges of the MR sensor and other layers of the read head form an air bearing surface (ABS). When a magnetic disk is rotated by the drive, the slider and one or more heads are supported against the disk by a cushion of air (an xe2x80x9cair bearingxe2x80x9d) between the disk and the ABS. The air bearing is generated by the rotating disk. The read head then reads magnetic flux signals from the rotating disk.
There are two critical dimensions of the MR head, namely the trackwidth and resolution of the MR head. The capability of the MR head to read data recorded at high areal densities is determined by its trackwidth and its resolution.
The trackwidth of the MR read head is the length of the active or sensing region for the MR sensor and is typically defined by the photolithography and subtractive or additive processing. The trackwidth is defined by the recess generated by the photoresist PR used during a photolithography process.
Resolution, on the other hand, is determined by the gap of the read head which is the distance between the first and second shield layers at the ABS. Accordingly, this distance is the total of the thicknesses of the MR sensor and the first and second gap layers G1 and G2. When the first and second gap layers G1 and G2, which separate MR sensor from the first and second shield layers S1 and S2, become thinner, the linear resolution of read head becomes higher. A serious limitation on the thinness of the gap layers of the read head is the potential for electrical shorting between the lead layers and the first and second shield layers. The thinner a gap layer, the more likely it is to have one or more pinholes which expose a lead layer to a shield layer. Pinholes can significantly reduce the yield of a production run of MR read heads.
It is important to note that the only place where the gap layers have to be thin is in an MR region where the MR sensor is located. The gap layers can be thicker between the lead layers and the first and second shield layers. Accordingly, it is desirable if each gap layer could be thin in the MR region to provide high linear resolution and thick outside of the MR region to provide good insulation between the lead layers and the shield layers.
The MR read head of FIG. 1 accomplishes this using a two step process of depositing first gap layers before the MR sensor is deposited and a two step process of depositing second gap layers after the MR sensor is deposited. In the present device, a very thin first gap layer G1 is deposited on the first shield layer S1. An MR region is then masked and a first gap pre-fill layer G1P, which may be thicker than G1, is deposited. The mask is removed, leaving the first gap pre-fill layer G1P everywhere except in the MR region. Lead layers L1 and L2 and an MR sensor are then formed.
Next, a very thin second gap layer G2 is deposited. The MR region is then masked and a second gap pre-fill layer G2P is deposited. After lifting off the mask, the G2P layer is located everywhere except in the MR region. The result is that very thin G1 and G2 layers are in the MR region at the bottom and top of the MR sensor to provide the MR head with a high linear resolution, the G1 and G1P layers are located between the heads and the first shield layer S1 to prevent shorting between the lead layers and the first shield layer S1, and the G2 and G2P layers are located between the lead layers and the second shield layer S2 to prevent shorting between the lead layers and the second shield layer S2.
As such, the present device is capable of providing a read head which has a very thin gap layer at the MR region, and yet will prevent shorts between lead layers and the first and second shield layers.
Despite this, the MR read head of FIG. 1 includes gap layers G1, G1P, G2, and G2P which afford many non-planar surfaces in the form of beveled edges circumnavigating the MR sensor. Such non-planar surface must, in turn, be subjected to photoresist layers during processing. Due to inherent limitations of photolithography, two problems result which compromise control of the critical trackwidth and resolution dimensions.
First, the beveled edges cause reflective notching due to light scattering. See arrows in FIG. 1. Secondly, the non-planar surfaces cause non-uniform photoresist coverage during processing which, in turn, invokes the well known xe2x80x9cswing curvexe2x80x9d effect. FIG. 2 illustrates the manner in which the critical dimensions (trackwidth and resolution) vary as a function of photoresist thickness, in accordance with the swing curve effect. As is well known, the constructive and destructive interference of reflected light within the photoresist film causes the swing curve effect.
Prior art devices have attempted to overcome the foregoing disadvantages through the addition of antireflective layers and planarization. Unfortunately, antireflective layers are only partially effective and introduce complications associated with their removal.
There is therefore a need for an MR read head with an improved gap layer which utilizes planar surfaces to avoid adversely affecting the MR region, while providing a thin gap layer adjacent to the MR region and a thick gap layer between lead layers and the first and second shield layers.
It is an object of the present invention to disclose a magnetoresistive (MR) read head with an improved gap layer which does not adversely affect the MR region.
It is another object of the present invention to disclose an MR read head which has a very thin gap layer adjacent to the MR region.
It is still another object of the present invention to disclose an MR read head which has a very thick gap layer between lead layers and the first and second shield layers of the MR read head.
It is still yet another object of the present invention to disclose an MR read head which has gap layers that are planar to avoid the negative ramifications of reflective notching and the swing effect.
These and other objects and advantages are attained in accordance with the principles of the present invention by disclosing an MR read head including a shield layer with a recessed portion and a protruding portion defined by the recessed portion. Also included is an MR sensor located in vertical alignment with the protruding portion of the shield layer. Further provided is at least one gap layer situated above and below the MR sensor. At least one of such gap layers is positioned in the recessed portion of the shield layer.
In one embodiment of the present invention, the gap layers may include a first gap layer located on top of the recessed portion of the shield layer. Such first gap layer may include an upper surface substantially level with an upper surface of the protruding portion of the shield layer. As an option, the recessed portion of the shield layer may be formed by an etching process.
The gap layers may further include a second gap layer located on top of the first gap layer and the protruding portion of the shield layer. The MR sensor may be located on top of the second gap layer. As a result of the aforementioned underlying structure, an upper surface of such second gap layer may be planar to avoid the negative ramifications of reflective notching and the swing effect.
In addition to the first and second gap layers, a third gap layer may be located on top of the MR sensor.
To this end, a combined thickness of the first gap layer, second gap layer, and third gap layer is thinner adjacent to the MR sensor and the protruding portion of the shield layer than the recessed portion of the shield layer for insulation purposes.
In yet another embodiment, a method is provided for fabricating the MR read head. Initially, a shield layer is deposited. Thereafter, a recessed portion is etched in an upper surface of the shield layer. Such recessed portion of the shield layer defines a protruding portion of the shield layer. A first gap layer is deposited on top of the recessed portion of the shield layer, and a second gap layer is deposited on top of the first gap layer and the protruding portion of the shield layer. Next, an MR sensor is positioned on top of the second gap layer in vertical alignment with the protruding portion of the shield layer. First and second lead layers are subsequently positioned on top of the second gap layer. The first and second lead layers are positioned such that they are connected to the MR sensor. A third gap layer is then deposited on top of the second gap layer, the MR sensor, and the first and second lead layers.